One approach to reducing vehicle weight in automotive design is with aluminum intensive vehicles (AIVs). AIVs have often been based on the unibody design of steel vehicle architectures, which are assemblies of stamped sheet components. Automotive AIV design has focused primarily on the 5XXX and 6XXX series aluminum sheet, as they can be shaped and processed by methods consistent with those already used in automotive manufacturing of steel sheet (e.g., sheet stamping, automated assembly, paint process). These alloys may have strengths equivalent to the mild steel sheet generally used in steel vehicle platforms. The 6XXX series aluminum alloys may experience improved mechanical strength properties when certain heat treatment processes are performed.
For some applications, multiple components, such as metal sheet, may be joined. One method for mechanically joining multiple components, such as 2T, 3T and 4T material stack-ups (e.g., 2, 3, or 4 sheets in a stack), may include the use of self-piercing rivets (SPRs). A SPR is a cold joining riveting process used to fasten two or more sheets of material by driving rivets through the top sheet(s), which may create a “button” on the bottom sheet. However, if the sheets do not have sufficient joinability or rivetability, then defects may occur in the sheets and/or the rivet. Examples of defects may include radial cracking of the rivet button, cracking in the side wall of the rivet button, a crack in the stack, or buckling of the rivet legs. In general, higher strength materials tend to have lower joinability. Therefore, joining processes, such as SPRs, may result in joining defects when multiple high strength components are joined.